Role of diet in cancer etiology.

Current evidence for the involvement of diet in cancer etiology is based on indirect relationships between the consumption of selected food constituents and incidence, dietary studies, and laboratory data. The indirect evidence most often referred to is the suggested correlation between the complex of fats-meat-egg-animal protein and the risk for cancer of the colon. Such observations are, however, hampered by the fact that human diet does not consist of isolated food components. Case control studies implicate a higher intake of starchy foods in gastric cancer, a lower intake of fiber in colon cancer, and possibly coffee in renal cancer. Carcinogenic agents identified include food additives, plant toxicants, aflatoxins, polycyclic hydrocarbons, nitrosamines, and certain normal major food constituents. The experimental evidence is augmented by studies indicating an inter-relationship between dietary constituents, intestinal flora, and bile acid metabolism. A synergistic action of ingested or metabolized carcinogens and a co-carcinogenic function of certain dietary components are suggested.